The present invention relates to a method and apparatus for automatically assembling an assembly consisting of a compression spring, a retainer for holding the compression spring in a compressed state, and a cotter for setting the retainer in a holding state so as to cause a shaft member slidably or pivotally provided to a main body to perform a predetermined operation, and is applied to automatic assembling of members around intake and exhaust valves of a cylinder head block of an engine for a vehicle or an industrial machine, and automatic assembling of frictional clutch members of OA equipment.
Conventionally, an intake or exhaust valve as a shaft member slidably arranged on an engine as a main body is provided with an assembly consisting of a compression spring, a retainer for holding the compression spring in a compressed state, and a cotter for setting the retainer in a holding state so as to close the valve.
The above arrangement will be described below with reference to accompanying drawings. FIG. 1 is a sectional view of a cylinder head portion of an engine taken along a plane passing through a valve, and FIG. 2 is a sectional view showing an assembling state of the cylinder head portion. As shown in FIGS. 1 and 2, a valve guide 10b is inserted under pressure in a valve axial hole 10a of a cylinder head block 10 as a main body, and an intake or exhaust valve 7 is held by the valve guide 10b to extend therethrough. A valve spring 1 as a compression spring for holding a closed state by its compression biasing force is fitted around the upper end portion of the valve 7, and is assembled in an illustrated state using cotters 5 and 6 and a retainer 4 at the upper end of the shaft portion of the valve 7. The above-mentioned assembling method allows assembling without using any fasteners (e.g., screws).
The above-mentioned holding principle will be described below with reference to an explanatory view of FIG. 3. When the valve 7 is slidably held by the cylinder head block 10 as a main body, the valve spring 1 as a compression spring arranged around the upper end portion of the valve 7 is set to have a length shorter than its free length, and generates a biasing force F1 for biasing the valve 7 in a direction to separate from the cylinder head block 10. The biasing force F1 generates a partial force F2 in a direction perpendicular to a tapered surface 4a of the retainer 4, thereby generating a partial force F3 (FIG. 3) in the cotters 5 and 6. The cotters 5 and 6 are respectively formed integrally with projections 5a and 6a each having a shape matching with a recess portion 7a formed on the valve 7, and are set in the illustrated holding state under the effect of the partial force F3.
In the above-mentioned state, the valve 7 is opened/closed by pressing a top portion 7t of the valve 7 downward against the compression force of the valve spring 1.
The above-mentioned assembling work of the cylinder head is an almost manual work (e.g., the cotters 5 and 6 are inserted by letting them to freely drop), resulting in poor workability. In addition, it is not easy to insert the cotters at the predetermined position, resulting in poor productivity. In particular, since recent engines for vehicles tend to have a multi-valve structure, i.e., tend to have four to five valves per cylinder, the complicated structure of the engine head block makes the work more difficult.
As disclosed in Japanese Utility Model Publication No. 63-37162, a valve assembling apparatus for assembling half-divided cotters to a temporary assembly obtained by assembling an intake/exhaust valve, a valve spring, and a retainer to an engine cylinder head is proposed. In this apparatus, cotters are grasped by a chucking pawl unit via a cotter guide member. When the retainer is pushed downward upon downward movement of a retainer pressing member, the cotter guide member is stopped by the upper end of the valve. The cotters are then assembled to the valve by forcibly fitting them by the chucking pawl unit and engaging them with a cotter engaging groove.
In OA equipment, an arrangement wherein a frictional clutch is provided to a paper convey mechanism so as not to apply an over-load to a driving source is known. In this case, the frictional clutch is assembled in advance as an independent member, and this independent member is manually assembled using fasteners, screws, and the like.